The present invention relates generally to a roller hearth kiln for firing material while it is being carried and more specifically to a system for detecting roller breakage or failure in a roller hearth kiln.
A roller hearth kiln so far used for firing ceramic material into compact, light-weight ceramic products such as tiles includes a tunnel form of kiln body formed of such materials as refractory brick or ceramic fibers. Within this kiln body, there are an array of rollers for carrying the material to be fired in the lengthwise direction, which are discretely arranged across the kiln body. These rollers are driven for rotation by a driving means located outside of a kiln casing.
Such a roller hearth kiln, when a roller or rollers therein fail or break down, has some difficulty in smoothly carrying the material being treated, because the broken roller or rollers form or forms a barrier. It is then required to detect such roller breakage promptly, thereby replacing the broken rollers by new ones. A conventional roller breakage detector such as one known from JP-B-56-14951 is designed such that, when some rollers break down, the overall roll array is axially moved by means of springs and this is detected by a proximity detector. Another sensor system that is known from JP-A-3-87592 includes an arrangement of semi-circular light shielding members mounted at the driven side ends of rollers. These light shielding members rotate in unison in normal roller operation, but they do not rotate in unison when the rollers do not operate normally. This is detected by light receptors and projectors.
A problem with the conventional system shown in JP-B-56-14951, however, is that the structure for supporting the rollers is complicated due to the provision of such means as metal sheets or springs at the driven ends of the rollers, thus needing special care as to how to support the rollers.
The prior art system set forth in JP-A-3-87592 also offers a problem. As illustrated in FIG. 4 as an example, when there is a failure of a roller that rotates at the position shown in FIG. 4A in normal operation, a roller piece 5a tilts down, as illustrated in FIG. 4B. Then, this roller failure cannot be detected by a photoelectric switch 20; in other words, light cannot normally be cut off. Another problem is that, as shown in FIG. 4C, much time and labor are needed for regulating semi-circular light shielding members mounted at the driven ends of several tens' rollers of a few hundred rollers 15 to the same angle of rotation.
In view of overcoming these problems, an object of the invention is to provide a roller breakage detector system used with a roller hearth kiln, which ensures to detect some roller breakage or failure with simple equipment but with no need of any special care as to how to support the rollers.